Desalting method of fuel oil

ABSTRACT

The present invention provides a method for the desalting of fuel oil by mixing the fuel oil and clean water, thereby separating and eliminating sodium salts and potassium salts contained in the fuel oil, and the method comprises separating a heavy portion including salt-containing water from the fuel oil which is a light portion, this heavy portion separated from the fuel oil being separated into water and a residue by an evaporator, the water being reused as a washing water and the residue being burnt to use the generated heat as a heat source for the evaporator, whereby the residue is decreased in volume and solidified to be made easy in the handling.

TECHNICAL FIELD

The present invention relates to a desalting method of fuel oil toseparate and eliminate sodium salts and potassium salts contained in thefuel oil.

BACKGROUND ART

In the desalting method of fuel oil, excepting a specific method, itwould be conventional and known to separate water and sludge from theoil by making use of centrifugal force or static electricity, but themixture of salt-containing water and sludge separated out of the oilhave been discarded, and moreover there is no treating device suitablefor the sludge comprising water, salts, heavy oil sludge and the like.

In the operation of desalting device, it is necessary to use cleanwashing water in an amount of about 1% based on the fuel oil, whichwater has never been reused in general. Accordingly, it was impossibleto set up a plant of this kind in such a region as a desert region orthe like where water is hardly available.

Further, as the separated heavy sludge containing both salts and water,there is no suitable treating device, and therefore any effectivetreating method has not yet been established.

A main object of the desalting is to eliminate sodium and potassiumsalts contained in fuel oil, which salts are mainly composed of sodiumchloride and potassium chloride formed by the bond with chlorine andexist in the fuel oil either in the form of solution in a small amountof water contained therein or in the form of fine solid. It is knownthat these salts are soluble in water and therefore the elimination ofsodium and potassium salts can be accomplished by washing the fuel oilwith water to transfer the sodium and potassium salts into washing waterand then separating the water from the fuel oil.

Referring to FIG. 1, a desalting apparatus of prior art is explained.Fuel oil 5 stored in a fuel oil tank 3 is led through a fuel oil pump 4to a sludge separator 1, in which water and sludge contained in smallamount in the fuel oil are separated as a heavy portion 6 from adesludge oil 7, taken out and then led to a waste water-treatingequipment. Into the sludge-removed oil 7 feed from the heavy portion 6is poured an emulsion breaker 10 from an emulsion breaker tank 8 througha pump 9, thereafter newly deionized clean water 13 is incorporatedthereinto from a clean water tank 11 through a pump 12, and then themixture is thoroughly mixed in a mixer 14 so as to dissolve saltscontained in the sludge-removed oil 7 in water. The mixed liquid is ledto a desaltor 2, in which a salt-containing water 15 is separated as aheavy portion from the oil, and then led to a waste water-treatingequipment. The oil freed from the salt-containing water 5 contains onlya very small quantity of salts and can be dealt with as a desalted fueloil 16. In this manner, however, newly deionized clean water must beused and moreover the treatment of the separated heavy portion is leftunsolved.

DISCLOSURE OF INVENTION

The present invention provides such a method that both the sodium andpotassium salts-containing water contained in the fuel oil, and thenewly added washing water which contains the sodium and potassium saltsin consequence are separated from the oil by a separator, and thereafterrefined by evaporation, whereby the recovered water can be usedrepeatedly as the washing water.

Further, according to the present invention, the salt and oil-containingheavy sludge separated from the fuel oil is burnt, whereby the generatedheat can be recovered by the device for evaporation of water, andmoreover the sludge troublesome in the handling can be solidified anddecreased in volume so that the handling thereof is made easy.

In general, the fuel oil contains about 1000 ppm of water, in which thesodium and potassium salts are dissolved. Accordingly, when it issubjected to sedimentation to separate a light portion and a heavyportion the salts-containing water and the sludge are separated as theheavy portion from the oil. In the desalting of fuel oil, the separatedoil is further washed with water newly added, followed by separationinto a light portion and a heavy portion according to the sedimentationmethod, whereby the elimination of sodium and potassium salts slightlypresent therein can be performed. In general, the amount of water to beadded in this stage is about 1% based on the oil. Thus, the sum of watercontained in the oil as described above and water which has been addedfor the washing and then separated, reaches as large as 1.1% based onthe fuel oil. Therefore, when the recovery percent of water from theseparated waste water reaches about 91% or more and the recovered wateris refined to decrease the sodium and potassium salts contained thereinto 1000 ppm or less, the resulting water can be reused as the washing,so that there can be established a desalting device which requires nowater supply from the outer system, in other words, there can beestablished a desalting device having a closed circuit in respect ofwater. In the refinement of water by the evaporation method, it is easyto decrease the sodium and potassium salts contained in the recoveredwater to 1000 ppm or less and it is also easy to increase the recoveryof water to 91% or more by a proper selection of evaporators. Thepresent invention is characterized by combination of the refining methodof the separated water by evaporation, and the desalting device. Furtherthe invention is characterized in that the refining of the separatedwater is carried out by evaporation and the evaporation residue is burntto recover the heat for the evaporator, and moreover decrease in thevolume, solidification and facilitation in the handling of the separatedsludge can be accomplished because the sludge is taken out as theincineration residue.

BRIEF EXPLANATION OF DRAWINGS

FIG. 1 systematically shows a device for the desalting of fuel oil inaccordance with a prior art, and

FIG. 2 systematically shows one embodiment of the desalting device forcarrying out the method of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 2, one embodiment of the device for carrying out thepresent invention is illustrated as follows. In FIG. 2, the same portionas in FIG. 1 is marked with the same symbol as that. The heavy portion 6separated through the sludge separator 1 is led to an oil separator 23to recover an oil as a recovered oil 24, and then mixed with thesalt-containing water 15 separated through the desaltor 2, and themixture is supplied to an evaporator 17. In the evaporator 17, themixture is heated by means of a heat medium 18, and a steam 20evaporated is heat-exchanged with the fuel oil 5 in a heat exchanger 21,thereby recovering the heat, and then condensed to form a condensedwater 22, which is stored in the clean water tank 11, and thereafterincorporated into the sludge-removed oil 7 as the clean water 13 throughthe clean water pump 12. On the other hand, a residue 19 freed fromwater through the evaporator 17 is led through a residue pump 26 to anincinerator 27, where the combustibles therein are burnt, so that theheat medium 18 to be cycled through a heat medium-cycling pump 25 isheated, and a combustion residue 28 decreased in volume is taken outfrom the lower part of the incinerator 27.

Although the above embodiment shows a case where the fuel oil is mixedwith clean water after sludge has been removed from the fuel oil, andthen subjected to desalting treatment, it is apparent by the aboveexplanation that the present invention can be applied also in such amanner that the fuel oil is firstly mixed with clean water and then thesludge and the salt-containing water are separated from the oil.

EXAMPLE

Using as fuel oil an untreated crude oil, Arabian Light, stored in atank, the desalting treatment was carried out in accordance with themethod of the present invention, and the following results wereobtained.

(1) Content of impurities in the crude fuel oil

Sodium: 5 ppm

Potassium: 0.4 ppm

Water: 1200 ppm

(2) Content of impurities in the fuel oil at the outlet of sludgeseparator

Sodium: 0.9 ppm

Potassium: 0.07 ppm

Water: 100 ppm

(3) Amount of the sludge taken out at the sludge

separator: 50 Kg

(4) Aids added before putting into the desalting device

Clean water: 10 Kg

Emulsion breaker: 0.02 Kg

(5) Content of impurities in the fuel oil at the outlet of desaltingdevice

Sodium: 0.4 ppm

Potassium: 0.01 ppm

Water: 90 ppm

(6) Amount of the oil and salt-containing water taken out at thedesalting device: 50 Kg

(7) Amount of condensed water recovered at the heat exchanger: 11 Kg

From the above results, it was found that the desalting method inaccordance with the present invention can be carried out only withinitially added water, and can rather produce surplus water.

As described above, the present invention provides a desalting methodcomprising combination of a device for the desalt of fuel oil withrecovery and refinement of the separated water in an evaporation manner,by which method a small amount of water contained in the fuel oil can berecovered, and the recovered water is reusable for the desalting in aclosed system so that the desalting device of fuel oil can be set upeven in a region where water is hardly available, and moreover thesludge discharged from the desalting device can be used for the recoveryof heat by incineration, and made easy in the handling because of thecombustion residue being decreased in the volume and solidified.

We claim:
 1. A desalting method of a fuel oil comprising mixing the fueloil and clean water and separating and removing a heavy portionincluding salt-containing water from said fuel oil which is a lightportion, putting the heavy portion including the salt-containing waterwhich has been separated from the fuel oil into an evaporator toseparate water and a residue from each other, evaporating and recoveringwater, and then reusing the water recovered by the evaporation as theclean water.
 2. The desalting method of fuel oil according to claim 1,wherein a heat transfer medium is used in the evaporator to evaporatewater, and wherein residue separated from the water is burnt in anincinerator, the heat from the burning of the residue used for heatingthe heat transfer medium used in the evaporator for evaporating water.3. The desalting method of fuel oil according to claim 1 or 2, whereinthe heavy portion and the fuel oil are separated by sedimentation. 4.The desalting method of fuel oil according to claim 1 or 2, wherein thefuel oil is separated from sludge contained in said fuel oil prior tomixing the fuel oil and clean water, and the sludge and the heavyportion which have been separated from the fuel oil are put into saidevaporator to separate water and a residue from each other.
 5. Thedesalting method of fuel oil according to claim 1 or 2, wherein the fueloil contains sludge, and the fuel oil containing sludge is mixed withthe clean water, sludge and said heavy portion are separated and removedfrom said fuel oil, and the separated and removed sludge and heavyportion are put into said evaporator to separate water and a residuefrom each other.
 6. A method of recovering and reusing water from thedesalting of fuel oil, comprising the steps of separating and removing aheavy portion including salt-containing water from the desalted fuel oilwhich is a light portion, putting the heavy portion including thesalt-containing water which has been separated from the desalted fueloil into an evaporator to separate water and a residue from each other,evaporating and recovering water, and then reusing the water recoveredby the evaporation to desalt further fuel oil.
 7. The method ofrecovering and reusing water from the desalting of fuel oil according toclaim 6, wherein a heat transfer medium is used in the evaporator toevaporate water, and wherein the residue separated from the water isburnt in an incinerator, the heat from the burning of the residue beingused for heating the heat transfer medium used in the evaporator forevaporating water.
 8. The method of recovering and reusing water fromthe desalting of fuel oil according to claim 6 or 7, wherein the heavyportion and the fuel oil are separated by sedimentation.